Turning nanocrystals on and off, forever
In 2021, scientists made the exciting discovery that lanthanide-doped nanoparticles could set off an extreme light-producing chain reaction. Now, with partial support from the EU-funded AETSOM project, they have succeeded in making them turn their light on and off deliberately and indefinitely. The research was published in the journal ‘Nature’. Organic dyes and fluorescent proteins used in applications such as optical memory and bioimaging usually blink randomly until they finally lose their ability to fluoresce, going dark permanently. This is called photobleaching. Lanthanide-doped nanocrystals, on the other hand, are remarkably photostable. As described in a ‘EurekAlert!’ news release, scientists working at the lab of study senior author Associate Prof. P. James Schuck of AETSOM project partner Columbia University, United States, had never seen one die in their many years of research. Then, in 2018, they observed a crystal go dark and then turn back on again. Further research led to the discovery that the blinking behaviour of lanthanide optical fibres could be controlled. To ensure that they had indeed found the first fully photostable, fully photoswitchable nanoparticle, the team used near-infrared light to darken and brighten the nanocrystals in different ambient or aqueous environments. After turning them on and off more than a thousand times, there was still no sign of degradation. “We can turn these particles, which don’t otherwise photobleach, off with one wavelength of light and back on with another, simply using common lasers,” observed study lead author Dr Changhwan Lee, a postdoctoral researcher at Columbia University.
Potential applications
As reported in the news release, the team showed how the nanoparticles can be used to write and rewrite patterns onto 3D substrates, which could help improve high-density optical data storage and computer memory in the future. “This indefinite, bidirectional photoswitching nanocrystal could yield an all-optical quantum memory device for storing the vast amount of data produced by quantum computers—think of CD-ROMs and CD-RWs, but faster and much more precise,” explains co-author Prof. Yung Doug Suh of the Korea Research Institute of Chemical Technology, South Korea. Besides advancing optical data storage, photoswitchable nanoparticles could open many other doors, driving a wide range of other technologies that range from super-resolution imaging and nanophotonics to targeted pharmacology, optogenetics and chemical reactivity. But what makes this possible? How does photoswitching happen in these nanocrystals? The team believes that, in their work, photoswitching is the result of atomic crystal defects so small that they cannot be seen even under the most advanced electron microscopes. “These defects shift the particle’s avalanche threshold up or down and can be toggled by different wavelengths of light to make the signal dimmer or brighter,” the news release reports. This study was completely unexpected, according to co-author Dr Bruce Cohen of Lawrence Berkeley National Laboratory in the United States. “We had been saying since our 2009 paper that this class of nanoparticles doesn’t switch on and off, and yet that’s exactly what we’re studying here. One of the things we’ve found with these nanoparticles is to embrace weird results.” AETSOM (Engineering a solution to the “resolution gap” problem for probing local optoelectronic properties in low-dimensional materials) is coordinated by The Hebrew University of Jerusalem. The project ends in August 2024. For more information, please see: AETSOM project
Keywords
AETSOM, nanoparticle, nanocrystal, light, lanthanide, photoswitching
